Support pre-standard DASH MIME type
Support pre-standard DASH MIME type

This adds support for a DASH MIME type that predates standardization
on "application/dash+xml".  Some servers still use the older, now
non-standard MIME type of "video/vnd.mpeg.dash.mpd".  This is trivial
to support, and it helps some folks who needs it, so there's no good
reason not to support it.

Change-Id: I17e85fdb74491e9e32628eddf30ef9e88acf5221

shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player